release-1.15: Reduce minimum go toolchain in go.mod and verify it do not lower toolchain used to build.

[kaovilai]

TL;DR: this change keeps 1.22.8 as go toolchain for this repo without enforcing it as minimum version on others.

Verification (click me!)

make container && docker run --rm velero/velero:main /velero version --client-only
[+] Building 60.0s (18/18) FINISHED                                                                                                        docker-container:colima-multiplat
 => [internal] load build definition from Dockerfile                                                                                                                    0.0s
 => => transferring dockerfile: 2.37kB                                                                                                                                  0.0s
 => [internal] load metadata for docker.io/paketobuildpacks/run-jammy-tiny:0.2.52                                                                                       3.6s
 => [internal] load metadata for docker.io/library/golang:1.22.8-bookworm                                                                                               3.4s
 => [auth] paketobuildpacks/run-jammy-tiny:pull token for registry-1.docker.io                                                                                          0.0s
 => [auth] library/golang:pull token for registry-1.docker.io                                                                                                           0.0s
 => [internal] load .dockerignore                                                                                                                                       0.0s
 => => transferring context: 60B                                                                                                                                        0.0s
 => CACHED [stage-2 1/3] FROM docker.io/paketobuildpacks/run-jammy-tiny:0.2.52@sha256:402b925a81a4c6985438fd37d0b22022ca688e528bbd46a38831a3702067cced                  0.0s
 => => resolve docker.io/paketobuildpacks/run-jammy-tiny:0.2.52@sha256:402b925a81a4c6985438fd37d0b22022ca688e528bbd46a38831a3702067cced                                 0.0s
 => CACHED [restic-builder 1/3] FROM docker.io/library/golang:1.22.8-bookworm@sha256:3f0457a0a56a926d93c2baf4cf0057a645e8ff69ff31314080fcc62389643b8e                   0.0s
 => => resolve docker.io/library/golang:1.22.8-bookworm@sha256:3f0457a0a56a926d93c2baf4cf0057a645e8ff69ff31314080fcc62389643b8e                                         0.0s
 => [internal] load build context                                                                                                                                       0.2s
 => => transferring context: 883.86kB                                                                                                                                   0.2s
 => CACHED [velero-builder 2/4] WORKDIR /go/src/github.com/vmware-tanzu/velero                                                                                          0.0s
 => [velero-builder 3/4] COPY . /go/src/github.com/vmware-tanzu/velero                                                                                                  1.6s
 => [restic-builder 2/3] COPY . /go/src/github.com/vmware-tanzu/velero                                                                                                  1.6s
 => [velero-builder 4/4] RUN mkdir -p /output/usr/bin &&     export GOARM=$( echo "" | cut -c2-) &&     go build -o /output/velero     -ldflags "-X github.com/vmware  49.7s
 => [restic-builder 3/3] RUN mkdir -p /output/usr/bin &&     export GOARM=$(echo "" | cut -c2-) &&     /go/src/github.com/vmware-tanzu/velero/hack/build-restic.sh &&  34.6s
 => [stage-2 2/3] COPY --from=velero-builder /output /                                                                                                                  0.2s
 => [stage-2 3/3] COPY --from=restic-builder /output /                                                                                                                  0.1s
 => exporting to docker image format                                                                                                                                    4.1s
 => => exporting layers                                                                                                                                                 2.7s
 => => exporting manifest sha256:5387d1a59b10970f9d0800ba960c4eb0f008e0d2bba5a9498b009ac478e5f4d4                                                                       0.0s
 => => exporting config sha256:f29cee5131777c8dc47571fc475f1abb2984ff1657b51c3a720c8aa453b195f2                                                                         0.0s
 => => sending tarball                                                                                                                                                  1.4s
 => importing to docker                                                                                                                                                 0.5s
 => => loading layer 4e2166c05ab9 491.52kB / 45.94MB                                                                                                                    0.5s
 => => loading layer dd8fc23784d7 98.30kB / 8.82MB                                                                                                                      0.1s

 1 warning found (use --debug to expand):
 - UndefinedVar: Usage of undefined variable '$GOPROXY' (line 58)
container: velero/velero:main
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
Client:
        Version: main
        Git commit: 303d239819259b54ecd264eef176b9dc55db3871-dirty
        Go version: go1.22.8

Thank you for contributing to Velero!

Please add a summary of your change

Reduce minimum go toolchain + add verification from #8398

Does your change fix a particular issue?

Fixes #8397

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: Patch coverage is 10.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 58.98%. Comparing base (1d4f147) to head (d083d39).
Report is 2 commits behind head on release-1.15.

Files with missing lines	Patch %	Lines
pkg/buildinfo/buildinfo.go	0.00%	8 Missing ⚠️
pkg/cmd/server/server.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.15    #8399      +/-   ##
================================================
- Coverage         58.99%   58.98%   -0.02%     
================================================
  Files               367      367              
  Lines             38847    38856       +9     
================================================
+ Hits              22918    22919       +1     
- Misses            14467    14475       +8     
  Partials           1462     1462              

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